As an also-over-35, I don't think it's just the alcohol. (Feel free to slap me down with science.) A beer hangover is now more severe than an equivalent-amount-of-alcohol hangover from say, vodka.
Someone told me that it's because you consume too much fluids when drinking beer, causing mineral and vitamin imbalances or some such. (I ain't no scientalist!) This makes sense if true, since to reach the same level of alcohol in your blood you simply have to drink more beer than say vodka, which is obviously much stronger.
Some more anecdotal evidence. I've noticed that the style/quality of the beer greatly affects if there will be a hangover or not regardless of alcohol content. Has anyone else noticed that? or know why?